1. Field of the Invention
This invention relates to a method for evaluating a gloss and brightness character of a coated paint film, and more particularly to such a method for obtaining numerically estimated values representing the gloss and brightness character, with the numerical having good correlation to corresponding organoleptic values.
2. Description of the Prior Art
It has been well confirmed from a variety of studies, that uneveness of the surface of a coated paint film is a composite wave compound of a variety of waves having frequencies ranging from several .mu.m to several cm. Accordingly, the sensory perception of the composite wave in each of the respective frequency ranges are different from one another. Additionally, it is also confirmed that the causes for the formation of the waves are different from each other in accordance with the frequencies. Therefore, in order to evaluate the result of the coated paint film and to feedback the result to a production process of automotive vehicles, it is necessary to independently quantify the degrees of unevenesses having a variety of ranges of frequencies.
Known systems for evaluating the uneveness of the surface of a coated paint film or the like are arranged to make measurement upon contact with the surface of the coated paint film. Accordingly, employing such evaluating systems renders impossible an evaluation of the paint film coated on a surface having a variety of curvatures such as a vehicle body panel, and also renders impossible an automatic inspection for the coated paint film in a production process of the automotive vehicles. Additionally, in any of the above conventional evaluating systems, it is impossible to obtain a broad field of view for evaluation, so that there arises a scattering in evaluation values, while also making detection of uneveness in the order of several cm impossible.
In order to solve the above problems, methods for quantifying the gloss and brightness character of a coated paint film are disclosed in Japanese Patent Provisional Publication Nos. 58-97608 and 61-217708. In these methods, a rectangular pattern is projected onto the surface of a coated paint film. The reflected light of the projected pattern is received by a one-dimensional photoelectric element. The diffusion condition of the reflected light is quantified by using a power spectrum upon a Fourier transform. In addition, it has recently been proposed to process a two-dimensional image as disclosed in Japanese Patent Provisional Publication Nos. 1-210806, 1-210807 and 1-213509.
However, difficulties have been encountered in the above conventional systems and methods for evaluating the gloss and brightness character of the coated paint film, in which a mechanism for detecting and analyzing the surface condition of the coated paint film is considerably different from that based on human's visual observation, so that resulting evaluation values are not in correlation to those based on the human's visual observation. Additionally, it is difficult to measure or evaluate the gloss and brightness character when the surface of coated paint film has a relatively large curvature, for example, in case of the paint film coated on a vehicle body. Furthermore, it has been also problematic that the resulting evaluation values are unavoidably scattered in a wide region, even in measurements or evaluations in the same condition. Thus, the above-discussed conventional systems and methods for evaluating the gloss and brightness character of the coated paint film are problematic from the practical view points.